Fracture behavior of silica nanoparticles reinforced rubber/epoxy composite

Hybrid composites consisting of soft rubber (carboxyl-terminated butadiene acrylonitrile, CTBN) and silica nanoparticles with average particle size of 20 nm were studied for improving toughness of epoxy resins (diglycidyl ether of bisphenol A, DGEBA). The hybrid carboxyl-terminated butadiene acrylonitrile /silica nanoparticles epoxy systems exhibited improvements in the Young’s modulus, and more importantly, fracture toughness (K_IC), which can be explained by synergistic impact from the inherent characteristics of each filler. In this study, the highest K_IC was reached with addition of small amounts of silica nanoparticles (5 vol.%) to the epoxy containing 15 vol.% carboxyl-terminated butadiene acrylonitrile, where the K_IC was distinctly higher than with the epoxy containing carboxyl-terminated butadiene acrylonitrile or silica nanoparticles alone. Cavitation of rubber particles with matrix dilation and particle debonding with subsequent void growth were determined as the toughening mechanisms responsible for the toughness improvements for epoxy. The evidence indicates that debonding of the silica nanoparticles causes a weakening of the matrix–particle interface. The toughness enhancement in hybrid nanocomposites involves an increase in silica nanoparticles particle debonding an increase in plastic zone size, which allows the epoxy matrix to dissipate more fracture energy.